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. 2015 Jul 16;10(7):e0129700. doi: 10.1371/journal.pone.0129700

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© 2015 Borghans et al

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.

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Fig 1 — Note: Tests 1 was taken in January 2007. Test 2 was taken in May or June 2007. Test 3 was taken in January 2008, and Test 4 was taken in May or June 2008. Tests one and two contain the same questions. Tests three and four also contain the same items. Children had, on average, six months of schooling when taking the first test. The average time that elapsed between the first two tests in grade one of preschool is 4.3 months, and 3.9 months passed between tests three and four in grade two of preschool. The average time that passed between tests one and four is 16.3 months.